I make no attempt at a complete and detailed history here. A full history could fill thousands of pages or more. I will just have some representative material, things that a native of Krosa might have come across.
Gods and magic come into the world. Lots of funky non-human races created. They fight, they multiply, they use high-powered magic.
Everyone dies.
Start all over again, with less power this time. Various civilizations form. Krosa becomes a major power. Prospers. Happy.
Evil king Zohak takes over Krosa. Demonic. All the Krosans follow him into depravity or get killed messily.
A hero (Feridun) kills Zohak. The gods smite Krosa. All that's left is an itty bitty island in the Indian Ocean.
That's where your character lives.